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materials and engineering > Chapter 6-the rest > Flashcards

Chapter 6-the rest Flashcards

1
Q

Casting

A
  • In the casting process, metals are first melted in a furnace.
  • Alloying elements are then added and thoroughly mixed
    (magnesium is added to aluminum to produce a stronger and
    lighter alloy).
  • Oxide impurities and unwanted gasses are removed.
  • The melt is then poured into a mold and chilled to solidify
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2
Q

recrystallization temp

A

Used in hot rolling where materials are heated to a high temp

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3
Q

% cold work

A

= [(initial metal thickness- final thickness)/ initial thickness] x 100

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4
Q

extrusion

A

metal workpiece (billet) is placed under high
pressure using a ram and forced through opening in a die

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4
Q

indirect extrusion

A

experiences lower friction on the billet and
therefore needs less power however has a limit on the applied
load

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5
Q

direct extrusion

A

produces products such as cylindrical rods, tubes,
and with some metals more irregular shapes

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6
Q

forging

A

metal is hammered into a desired shape

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7
Q

open die

A

Dies are either flat or
simple in geometry

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8
Q

closed die

A

Dies have upper
and lower impression – more complex

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9
Q

wire drawing

A

the starting rod or wire is drawn through
several drawing dies to reduce diameter

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10
Q

cold work of wire drawing

A

= (Change in cross-sectional area/ original area) x 100

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11
Q

elastic deformation

A

Atoms elongate resulting in overall elongation of the specimen. But
return to their original dimensions after tensile force is removed,
resulting in recoverable deformation

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12
Q

plastic deformation

A

Atoms break bonds and slip on each other.
Once slip occurs, atoms can not return to their original positions, resulting in permanent deformation.

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13
Q

normal stress σ

A

=(F -> avg uniaxial tensile force)/ (Ao -> original cross-sectional area) (lb/in^2 or N/m^2)

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14
Q

Normal strain ε

A

=Change in length/ original length

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15
Q

shear stress τ (parallel to surface)

A

=(S -> shear force)/ (A -> area of application)

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16
Q

shear stress γ (change in shape)

A

= amount of shear displacement a/ distance h over which stress acts = tan θ

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17
Q

linear elastic range

A

linear portion of the stress strain curve

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18
Q

yield point

A

The point on the curve when the elastic range ends

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19
Q

ultimate tensile strength σu

A

the largest stress the
specimen can take before fracture

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20
Q

Fracture point

A

The point on the curve where the specimen fails

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21
Q

Modulus of elasticity (E)

A

Stress and strain are linearly related in the elastic region. (Hooke’s law)

= stress/ strain

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22
Q

poisson’s ratio is always positive

A

= -[(w-wo)/ wo] / [(l-lo)/lo]

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23
Q

Yield strength

A

the stress at which
a material begins to experience
permanent or plastic deformation

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24
Q

% elongation fracture

A

a measure of ductility of a
material

= (final length- initial length)/ initial length

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25
Q

modulus of resilience Ur

A

measure of the amount of
energy needed to cause yield in the material

=1/2 (σy-Ey)

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26
Q

toughness

A

amount of energy required
to fracture the material. It is a measure of combination of strength and ductility

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27
Q

true stress and true strain

A

are determined based on instantaneous
cross-sectional area and length of the specimen

28
Q

hardness

A

a measure of the resistance of a metal to localized
plastic deformation or indentation

29
Q

slip bands

A

Plastic deformation in a single crystal results in formation of bands

30
Q

slip

A

caused by application of shear stress on the grain.
The mechanism by which slip occurs is by formation of
dislocations and their movement

31
Q

unit step of slip

A

created Once the dislocation reaches the
end of the grain

32
Q

resolved shear stress (shimid’s law)

A

Tr=σ(cosλ cosθ)

33
Q

critical resolved stress

A

the shear stress required to
cause slip in a single crystal

34
Q

twin

A

part of atomic lattice is deformed and forms
mirror image of lattice next to it

35
Q

hall-petch equation

A

=σy = σ0 + k/d^1/2
σy= yield strength
σ0 and k are constants
d is avg grain size diameter

36
Q

solid solutions

A

addition of one or more impurity (solute) to
the host metal can increase the strength of metals

37
Q

annealing

A

heat treatment
process applied to a strain-
hardened or cold-worked
metal to remove residual
stresses, grow new equiaxed
grains and soften the metal

three stages of the
annealing process are:
recovery, recrystallization and
grain growth

38
Q

polgonization

A

Dislocations rearrange themselves to
form lower energy configurations

39
Q

composite

A

combination of two or more individual materials designed to obtain more individual properties

40
Q

composite phase types

A

– Matrix - is continuous
– Dispersed - is discontinuous and surrounded by matrix

41
Q

Composite Types:

A

Particle reinforced
Fiber reinforced
structural
nano

42
Q

Particle reinforced

A

– Types: large-particle and dispersion-strengthened
– Properties are isotropic

43
Q

fiber reinforced
can be continuous (aligned) and discontinuous (aligned or random)

A
  • Fibers very strong in tension
    – Provide significant strength improvement to the
    composite
    – Properties can be isotropic or anisotropic
44
Q

structural

A
  • Laminates -
    – stacked and bonded fiber-reinforced sheets
  • Sandwich panels
    – honeycomb core between two facing sheets
45
Q

pultrusion

A
  • Continuous fibers pulled through resin tank to impregnate fibers with
    thermosetting resin
  • Impregnated fibers pass through steel die that preforms to the desired shape
  • Preformed stock passes through a curing die that is
    – precision machined to impart final shape
    – heated to initiate curing of the resin matrix
46
Q

filament windind

A

– Continuous reinforcing fibers are accurately positioned in a predetermined
pattern to form a hollow (usually cylindrical) shape
– Fibers are fed through a resin bath to impregnate with thermosetting resin
– Impregnated fibers are continuously wound (typically automatically) onto a
mandrel
– After appropriate number of layers added, curing is carried out either in an
oven or at room temperature
– The mandrel is removed to give the final product

47
Q

Ceramic Materials

A

Clay
glass
refractories
carbon
abrasives
cements

48
Q

Die blanks

A

– Need wear resistant properties!
* Die surface:
– 4 μm polycrystalline diamond
particles that are sintered onto a
cemented tungsten carbide
substrate

49
Q

refractories

A
  • Materials to be used at high temperatures (e.g., in
    high temperature furnaces)
50
Q

Ceramics

A

the bonding between the atoms is generally covalent or ionic, and they are much stronger than the metallic bonds.
 Hardness, thermal and electrical resistance are significantly higher than in metals.
 Ceramics are available in single-crystal and polycrystalline form.
 Finer grain size ceramics have higher strength and toughness.

51
Q

phase change

A

the structure of a material
changes from one form to another.

52
Q

phase

A

A region in a material that has a uniform structure, properties, and composition and maintains a distinct boundary with other unlike phases.
Ex: ice, water, vapor

53
Q

equilibrium

A

The state of a system when all forces and energies are balanced resulting in a stable system with no tendency to change with time

54
Q

phase diagram

A

Graphical representations of phases present in a material system at different temperatures, pressures and compositions.

Are developed based on assumption of equilibrium conditions resulting from slow cooling (equilibrium is approached but never fully maintained)

55
Q

triple point

A

point at which the 3 stages of matter coexist

56
Q

The number of phases that can
co-exist in equilibrium in a given system.
* P+F = C+2

A

P = number of phases that coexist in a system
C = Number of components
F = Degrees of freedom

57
Q

cooling curve

A

Temperature of molten metal is recorded versus time as
it cools to room temperature,
Every time there is a phase change, there is a change in slope.

For a pure metal, the cooling curve shows a flat region (plateau) at a specific temperature where liquid transforms to
solid

58
Q

In plateau region:

A

there is a mixture
of two phases in equilibrium.

59
Q

In a phase diagram:

A

Created from a series of cooling curves.
* Above the “start” line, the alloy is all liquid.
* Below the “finish” line, the alloy is all solid.
In the region between start
and finish, a mixture of solid
and liquid exists

60
Q

liquidius

A

The line that indicates start of
the solidification process

61
Q

solidus

A

The line that indicates completion of the solidification process

62
Q

binary isomorphous
system

A

a system where the two components are completely soluble in each other in both liquid and solid states (they do not from a third phase)

63
Q

Tie line

A

In the mixture region (L + α), the composition of both liquid (L) and solid (α) phases at any temperature can be determined by drawing a tie line

64
Q

Wo

A

Overall alloy composition

65
Q

Wl

A

The composition at point L is the composition of liquid, in the
mixture.

66
Q

Ws

A

The composition at point S is the composition of solid, in the
mixture.

67
Q

The amount of each phase can be determined through application of the Lever Rule:

A

Wt fraction of solid phase = Xs= (Wo-Wl)/(Ws-Wl)

Wt fraction in liquid phase= Xl= (Ws-Wo)/(Ws-Wl)

materials and engineering (1 decks)

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